Threaded fastener



April 12, 1938.

THREADED FASTENER Filed April 19, 19,37 2 Sheets-Sheet 1 fllllllll c.y G. oLsoN 2,113,600 v April 12, 193s f c. @OLSON y2,113,600

` THREADED FASTENER Filed April 19, 1937 2 shams-sheetv 2 56 y I EaZ/wr Caf Gi on) gay @ya Patented Apr. 12, 1938 PAT-ENT ori-lcs i mailman FAsTENsa `Carl G. Olson, Chicago, Ill., assigner to Illinois Tool Works, Chicago, lll., a corporation of Illinois Application April i9, 1937, Serial No. 137,720

14 CIS.

This invention relates generally to threaded fasteners, and more particularly to threaded fasteners of the self-tapping type provided with rolled threads. f It is an important object of the present invention to provide a tapping or thread-forming screw which is so constructed at the entering end thereof as to materially facilitate its initial application to an unthreaded aperture in a work piece.

A further object of the invention is to present `a screw, as set forth above, in which the thread on the thread-forming extremity and the juxtapositioned core portions of the screw present a novel construction which materially contributes toward the efficient functioning of the screw when applied to an unthreaded aperture in a work piece.`

More specifically the present invention conthereof at the entering extremity tapers reversely with respect to the thread taper in that vicinity. That is to say, a screw in which the core becomes larger toward the entering end and the 5 external or crest diameter of the thread thereon decreases.

Still another object of the invention is to pro-V of the lower section of the tapping screw, saidview being taken from the rear of Figure 1;

Figure 3 is a bottom elevational view of the screw shown in Figure 1 to more clearly illustrate the disposition of the longitudinal recess therein; Figure 4 discloses a fragmentary portion of the -screw during its initial thread-forming or tapping operation within a work piece, the associated parts being shown in section to more clearly illustrate the invention; Figure 5 discloses a fragmentary portion of a screw blank and thread rolling die to more clearly illustrate the manner in which the thread templates a screw in which the core portion on the thread-forming or tappingportion of the screw is formed;

Figure 6 discloses a modified thread-formingv screw contemplated by the present invention in which the crest diameter of the thread convolu- ,5 ,tions at the entering end -of the screw are u'niform, said screw being provided with a multiple as distinguished from a single thread;

Figure 7 is a view similar to Figure 4 disclosing the manner in which the screw of Figure 6 is initially applied to an unthreaded aperture of a work piece; l Figure 8 presents still another modified screw contemplated by the present invention inv which the thread is sharper than the standard machine screw thread, the screw in all other respects conforming with the screw shown in Figure 6; and Figure 9 discloses a fragmentary portion of a screw blank and thread rolling die -to illustrate the manner in which the screw of Figure 6 may be formed.

Referring now to the drawings more in detail, wherein like numerals have been employed to designate similar'parts throughout the various gures, it will be seen that one embodiment of the invention comprises a screw designated generally by the numeral it (Figures l. to 4 inclusive). This screw ili includes a suitable head it formed integral with a threaded body portion designatedgenerally by the numeral it. The body it is provided with a conventional machine screw thread along the holding portion indicated by the bracket A in Figure 1. The crest diameter of the thread decreases along the thread-forming or tapping portion indicated by the bracket B in Figure 1, said thread along the portion -B also decreasing in height with respect to exposed core portions i6. A suitable recess i8, extending longitudinally of the threaded body, separates the entering extremity of the screw into a screw section 20 having a serrated cutting edge 22, and a screw section `24 which is adapted to yieldl toward ythe section 20 when the screw is initially inserted Within an unthreaded aperture, the yielding of the section 24 serving to increase the cutting effectiveness of the serrated edge 22.

Particular attention is directed to the thread construction along the tapping or thread-forming portion B. The conventional machine screw thread extending along the holding portion A is of uniform height and conforms with any one of the conventionall standard machine screw specifications. In other words, the thread on they holding portion is of conventional or standard V-shaped cross section. It will be noted that the f2 2,113,6oo

exposed core portions I6 begin at the upper ex-- tremity of the tapping section B and increase in axial width toward the entering extremity of the screw. These exposed peripheral core portions not only increase in axial width toward the entering end of the screw, but also increase in diameter as they approach the entering end of the screw. 'Ihis is a structural feature which distinguishes the screw structurally and functionally from commercial forms `with which I am familiar, namely, those forms in which the root diameter remains constant or decreases in diameter along the entering or thread-forming portion.

It will be apparent from the foregoing description that the core or body portion of the screw tapers reversely with respect to the tapering of the juxtapositioned thread convolutions. 'I'hat is to say, as the crest diameter of the thread convolutions on the tapping or thread-forming portiondecreases, the diameter of the juxtapositioned core portions increases. tapering characteristics of the thread and screw body will be apparent from the dot-and-dash lines disclosed in Figure 2.

Attention is also'directed to -the fact that the axial pitch of the thread on the screw I is uniform along both the holding portion A and the thread-forming or tapping portion B. Although the height of the thread on the tapping portion B decreases with respect to the core diameter, lthe cross' sectional contour of the thread portion which is exposed, is uniiorm= with the corresponding exposed portions of the other thread convolutions. Thus, it may be said that the crown of the thread convolutions along the holding and thread-forming or tapping portions. remains constant and that the included angle oi.'

the thread indicated by the letter C (Figure 1) remains constant throughout the entire length of the screw. By reason oi' the foregoing thread construction on the tapping portion, the initial thread-forming or cutting operation takes place along a helical path which is disposed centrally with respect to the complete thread which is nally formed in the work. Thus, the cutting actioncaused by the cutting edges presented on opposite sides of each thread convolution is uniform because thethread is positioned centrally with respect to the complete helix ultimately produced in the work.

l Referring to Figure 4, it will be seen that I vprefer to insert the screw in an aperture 2l of a work piece 28 which is substantially equal in diameter to the external diameter of the entering extremity of the core I6, ,said diameter being indicated by the letter D in Figure 2. Thus, the exposed core diameter at the entering end provides a gauge which may be used to determine the size of the hole required for the screw. It will be understood that screws of the type disclosed herein are hardened` sufficiently to enter relatively hard substances, such as metal, without causing any injury or deformation to the thread convolutions. Furthermore, the holding power or capacity of a screw depends upon the stress required to shear the thread either' on the screw or in the work, `or both. In screws of the type disclosed herein the material of the screw is always, stronger than the material vof the work. Therefore, in subjecting a screw toa strain which is sufficient to strip the thread, this stripping occurs in the softer material, namely the work, and it will be evident that the stripping must occur at the root oi the thread in 'I'hese reverse whether the thread is of full depth, or partial depth and it has been proven that the holding power of a screw is nearly as great with twentyfive per cent thread engagement as it is with full thread engagement provided there is a sufiicient number of thread convolutions engaged. In using screws of the type shown herein it is only necessary, therefore, to employ an aperture, such as the aperture 26, which is considerably greater than the root diameter of the thread on the holding portion A. Hence. 'it is possible to employ the entering portion of the exposed core i6 as a gauge for the size of hole to be used in the work.

By having the above described reversed tapered relationship of the thread a'nd exposed core portionsat the entering end of the screw, I am able to prevent inadvertent loss of the screw should it become loosened. As the threads on the screw continue to form the complementary thread in the work 28, there is always a tendency for burrs and thelike to form which causes a slight reduction in the internal diameter of the aperture 26 after the screw has been ilnally driven home.

In other words, after the head I2 has been,

turned sufficiently so as to be clamped against a work piece 30, the aperture 26 will have been slightly reduced in diameter due to the presence of burrs and the like resulting from the cutting action of the serrating cutting action 22. Hence the diameter of the aperture 26 in the vicinity of the full thread on the holding portion of the screw will be sufilcientlyless than the entering diameter D of the core body I6 so as to prevent the screw from being inadvertently .lost due to vibration, et cetera. The reverse taper dispo- ,sition oi the thread and core body materially reduces the possibility of losing screws from the work even though the screws may slightly back out of the aperture.

In Figure I have disclosed the'manner in which screws of the type shown in Figures 1 to 4 inclusive may be rolled. While the present' invention is not directed to the method of rolling the thread on the screw, it is of interest from a practical standpoint at least to observe how these screws may be produced. A thread rolling die cal over the portion indicated by the letter 4A and is tapered over the portion indicated by e letter B, said portions corresponding with t e holding and tapping portions respectively oi' Figure l. In the actual rolling of the blank 34 a second die companion to and identicalwith the die 32 is employed, said blank being rolled between the two die blocks. When the blank has been rolled between the die blocks 32, the portion of the die blocks indicated by the-bracket E will' cause the reverse thread and core body arrangement, previously described, to be formed upon the portion B of the blank.

V Referring now to Figures 6 and 7, it will be seen that I have disclosed a modified screw construction indicatedgenerally by the numeral |0a.

and threaded body portion I4a. The thread on the body I4a is of conventional machine screw type and is a multiple thread as distinguished from -the single thread shown in Figure 1. The screw Illa is provided witha holding portion in- I, dicated by the bracket A, a thread-forming or This screw includes the usual head i2a' tapping portion indicated by the bracket B, and a piloting or guiding portion indicated by the bracket F. The crest diameter of the thread convolutions along the holding portion A are uniform and the height of the thread is uniform whereas the crest diameter of the thread along the thread-forming or tapping portion B decreases andthe height of the thread decreases with respect to exposed core portions la.. The thread convolutions along the section F are constant in crest diameter, but decrease in height with respect to the core portions ita. The peripheral exposed core surfaces ita increase in axial width toward the enterlng'end and also increase in external diameter toward the entering end of the screw similarly to the exposed core surfaces it of Figure 1. The screw body ld'a of the screw lila in Figure 6 is not provided with a longitudinal recess, but depends solely upon the imbedding action of the thread convolutions to form. a complementary thread in the work. In instances where the provision of a cutting 'edge will render the screw more emciently operable, a recess of the type shown in Figures 1 and 3 may be employed.

Referring to Figure 7, it will be seen that the screw lila is preferably applied to a wort: piece 2da in which an aperture ita corresponds in diameter with the crest diameter of the thread convolutions included within the area designated by the bracket i of Figure 6. By having this dimensional relationship between the crest diameter of the thread and the diameter oi the unthreaded aperture in the work, an operator may set the screw into the aperture oi the work before the screw is actually rotated to form a thread in the work. This type oi construction is particularly advantageous in instances where one operator inserts the screw within the hole and another operator subsequently `turns the screw into the work. Thus, the screw may he prepositioned and centered within the ,aperture of the work so as to facilitate subsequent tightenlng of the screw by the application ci a suitable turning tool, such as a power screw driver. The advantages incident to the use ci the screw lila are somewhat similar to those experienced in the use of screw ld. The screw its, being of the variety which operates on the indenting thread-forming principle as distinguished from the "cutting thread-forming principle, causes a material decrease in the diameter on the aperture 2da to take place. That'is to say, a considerable inward howing of the metal in the worin 2da takes place when the screw ita is. turned within the aperture 2da, and this material decrease in diameter cooperates with the exposed peripheral core portions in preventing the screw from being lost from the work piece. The size of the hole to be used in the wort. for the screwitc may be gauged by the crest diameter of the thread convolutions along the portion indicated by me brackets', rieur@ t.

In Figure B a further modified screw construction is shown which is designated generally by the numeralvitb. This screw is provided with any suitable conventional head ith formed integral with a threaded body Mb. The threaded l body Mb is provided with a holding portion A in which the thread is of constant height and uniform crest diameter, a thread-forming section B in which the thread decreases in crest diameter and decreases in height along exposed core surfaces I6b, and a guiding portion F wherein the crest diameter oi the thread is constant, the thread decreasing in height along the exposed peripheral core surfaces lsb. The screw Illb differs only from the screw loa in that the thread has a sharper included angle than the included angle indicated by the letter C in Figures l and 6. Thepincluded angle of the thread on the' screw illb ls indicated by the letter G in Figure 8. By having a relatively small included'angle G, the ease with which the screw will indent its way into`the work is enhanced.

In Figure 9, I have shown the manner in which a screw of the type shown in Figures 6 and 8 may be rolled. A pair of die blocks 36 disposed on opposite sides of a screw'blank 38 serve to roll vthe thread in the blank. It will `be noted that the blank is provided with a cylindrical section A, a tapering ,section B and a cylindrical section F. The serrations on the die block it, indicated by the bracket H, produce the thread convolutions on the thread-forming portion B of the screw and the portion of the dies it, indicated by the vbracket J, form the thread convolutions of constant crest diameter along the section F of the screw, l

From the foregoing description it will be apparent that my invention contemplates. a novel thread-forming or tapping screw in which the ease of insertion is materially enhanced. By

having the reverse taper arrangement, namely, a l vthread ywhich tapers in crest diameter reversely to the tapering of the juxtapositioned body or core diameter, advantages are obtained over many oi the present type commercial tapping screws. By employing the multiple thread construction, the crest of one thread convolution at the entering end of the-screw is positioned diametrically opposite the crest of a companion convolution. This diametrical disposition of the thread crests counteracts tendencies for the screw to cant when initially inserted within the self-threading fastener including a` thread forming V.portion decreasing in crest diameter toward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the corediarneter of the thread forming portion increasing toward the entering end.

'2. A self-threading fastener 'including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, and a head integral with the opposite extremity of said body, the crown along the holding and thread forming portions being of uniform cross-sectional contour, the thread on the thread forming portion decreasing in crest Vdiameter toward the entering end of 'the i fastener to"facllitate its initial application to an Unthreaded aperture inv a work piece, the core.

tremity thereof, and a head integral with the opposite extremity of said body, the thread along the holding and thread forming portions being of V-shaped cross-section, the thread on the thread forming portion decreasing in crest di- `ameter toward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end.

4. A self-threading fastener including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, and a head integral with the opposite extremity of said body, the crest of the thread on the holding and thread forming portions be-4 ing of uniform axial pitch, the thread on the thread forming portion decreasing in crest diameter toward the ventering end of the fastener `to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end.

5. A self-threading fastener including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, a head integral with the opposite extremity of said body, the thread on thethread forming portion decreasing in crest diameter t0- ward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end, and exposed peripheral core surfaces extending between thread convolutions on said thread forming portion.

6. A self-threading fastener including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, a head integral with the opposite extremity of said body, the thread 0n the thread forming portion decreasing in crest diameter toward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in'fa work piece, the core diameter of the thread forming portion increasing toward the entering end, and exposed peripheralcore surfaces of varying axial 'widths extending between ithread convolutions on said thread forming portion.

7. A self-threading fastener including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, and a head integral with the opposite extremity of said body, the thread on the thread forming portion decreasing in crest diameter toward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end, said thread forming portion being longitudinally recessed to present a cutting edge, the effective portion of said recess terminating short of the head.

8. A self-threading fastener including a threaded body having a holding portion and a hardened thread forming portion at one extremity thereof, and a head integral with the opposite extremity ofsaid body, the thread on the thread forming portion decreasing in crest diameter toward the enteringend of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end, the thread on said holding and thread forming portions being multiple to facilitate the insertion of the fastener.

, ward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end.

10. A self-threading fastener including a threaded body having a holding portion, a hardened thread forming portion and fa guiding portion extending beyond said thread forming portion, and a head integral with the opposite extremity of said body, the thread on the thread forming portion decreasing in crest diametertoward the entering end of the fastener to facilitate its initial application to an unthreaded aperture in a work piece, the core diameter of the thread forming portion increasing toward the entering end, the thread on the guiding portion being of constant crest diameter.

l1. A tapping screw fastener including a body having a threaded holding'portion and a hardened threaded tapping. portion at one extremity thereof, a head integral with the opposite extremity of said body, said tapping portion being longitudinally recessed to present a cutting edge, the effective portion of said recess terminating short of the head, the crown of the thread along the holding and tapping portions being of uniform cross-sectional contour and extending from the vicinity of the head toward the entering end of the fastener, the axial pitch of said thread -being uniform, the thread on the tapping portion gradually decreasing in crest diameter toward the 'entering end to facilitate its initial application to an unthreaded aperturein a work piece, and exposed peripheral core surfaces of varying axial widths extending between thread convolutions on said tapping portion, the diameter of said core surfaces increasing toward the entering end of the fastener.

l2. A tapping screw fastener including a body having a threaded holding portion and a hardened threaded tapping portion at one extremity thereof, a head integral with the opposite extremity of said body, said tapping portion being longitudinally recessed to present a cutting edge, the

effective portion of said recess terminating short of the head, the thread along the holding portion being of the machine screw type, the axial pitch of `said thread on the holding and tappingA portions being uniform, .the thread on the tapping portion gradually decreasing in crest diameter and cross-section toward the entering end to facilitate its initial application to an unthreaded aperture in a Work piece, and exposed peripheral core surfaces extending between thread convolutions on said tapping portion, the diameter of said core surfaces increasing toward the entering be`ing of the machine scre'w type, the axial pitch of said thread on the holding and tapping portions being uniform, the thread on the tapping portion gradually decreasing in crest diameter and cross-sectionl toward the entering end to facilitate its initial application to an Unthreaded aperture in la work piece, and exposed peripheral core'surfaces extending between thread convolutions on said tapping portion, the diameter of said peripheral core surfaces toward the entering extremity of the fastener being greater than the root diameter of the thread on the holding portion.

14. A tapping screw fastener including a body having a threaded holding portion and a hardened threaded tapping portion at one extremity thereof, a head integral with theI opposite extremity of said body, said tapping portion being longitudinally recessed to present a cutting edge, the

effective portion of said recess terminating short of the head, said, recess providing a yieldable screw section for increasing the cutting' effectiveness of said edge when the fastener is applied to an unthreaded aperture, the thread along the.l

holding portion being o; the machine screw type, the axial pitch of said thread onlthe holding and tapping portions being uniform, the thread on the tapping portion gradually decreasing in crest diameter and cross-section toward the entering end to facilitate its initial application to an unthreaded aperture in a work piece, and exposed peripheral core surfaces extending between thread convolutions on said tapping portion, the diameter of said peripheral core surfaces toward the entering extremity of the fastener being greater than the root diameter of vthe thread on the holding portion.

CARL G. OLSON. 

